Russia is suspected to have "neutralised" the GPS systems of a plane carrying European Commission President Ursula von der Leyen in Bulgaria.
The GPS jamming attack forced the Dassault Falcon 900LX plane to land using "terrestrial navigation tools" like paper maps and a compass on Monday local time, according to Bulgarian officials.
EU commission spokesperson Arianna Podestà said the jamming incident was suspected to be "blatant interference by Russia".
When asked about the allegations, a Kremlin spokesperson told the Financial Times, "Your information is incorrect."
The incident with Ms von der Leyen's plane joins a growing list of alleged acts of Russian interference with GPS satellite navigation.
Finland, Latvia, Lithuania, Estonia and other countries bordering Russia have warned of increased electronic activity interfering with flights, ships and drones.
Australian National University Centre of European Studies visiting fellow Matthew Sussex said Russia was "normally behind these types of GPS jamming attacks in Europe."
Professor Sussex said the attack aimed at the chief of the EU was "an escalation" in Russia's hybrid warfare.
Ms von der Leyen is currently on a four-day tour of Europe's eastern flank to speak to nations on the "frontline" of Russian hybrid threats.
"The EU will continue to invest into defence spending and in Europe's readiness even more after this incident," the EU confirmed.
What is GPS jamming?
The Global Navigation Satellite System (GNSS) is the term used to group satellite-based navigation systems, including the Global Positioning System, or GPS, which is a United States-run network of satellites.
GPS provides precise locations, time and altitude data to users.
GPS jamming uses ground-based signals to block or overpower the signal — and it is easy to do, according to Flinders University professor of wireless system security Sam Drake.
"It's extremely easy to do that with a few hundred dollars worth of equipment," Professor Drake said.
StrategicAir pilot and consultant director Tony Stanton said the satellites were in medium Earth orbit, about 20,000 kilometres above Earth.
He said by the time the radio frequency got to an aircraft, it was "very, very weak" and a person did not need "a very powerful transmitter of the same frequency to be louder than the satellite".
When a system is jammed, it might have to be switched off for the duration of the flight, which can cause delays to take-off and landing.
In terms of Ms von der Leyen's flight to Bulgaria, the GPS jamming caused approximately 10 minutes of delays.
"There was very little distraction to the aircraft in this case," Dr Stanton said.
Another form of GPS hacking is "spoofing", where an aircraft is sent a false signal so it has inaccurate location data.
"Spoofing is much more sophisticated and more dangerous … it is where the other signal actually tries to imitate the satellite signal and give it a false time or a false position," Dr Stanton said.
"What is dangerous about that is that [it] doesn't necessarily give an error alert to the pilot."
Does Russia do this a lot?
According to Professor Sussex, Russia does do this a lot.
"The Russians have been doing it since about 2014," he said.
"The Russians will try all sorts of means below the threshold of war, and GPS jamming is one of them that will make life difficult for Europeans."
These attacks were designed to show Europe that "no-one" was safe from Russia, he said.
The region had experienced "a lot of such jamming and spoofing activities", an European Commission spokesperson said.
The EU has sanctioned several companies believed to be involved.
In July this year, the International Civil Aviation Organization (ICAO) asked Russia to cease GPS interference.
ICAO said in their request to Russia that the disruptions had forced aircraft, ships, and drones to alter their routes.
Professor Sussex added that Russia would often pay criminals in different countries in Europe to do these kinds of attacks.
"They are often paid quietly through bitcoin but sometimes they are directly in contact with the Russian military intelligence or the FSB," he said.
EU Defence Commissioner Andrius Kubilius said the 27-nation bloc would increase its number of satellites in low orbit to enhance detection of interference.
Professor Sussex said Russia was sending the message that the longer the EU resisted, the worse these kind of attacks would get.
"It's reinforcing the Russian approach to be information operations, which is to convey the message we're present, we're everywhere and we can we can reach out and make life difficult for you," he said.
Could it happen in Australia?
In short, yes it could.
However Dr Stanton said there had been no major reported GNSS or GPS jamming events in Australia.
He said even if there was, all major Australian airports had conventional navigation aids for pilots to use if they needed to that did not rely on GNSS or GPS.
"I think ultimately it would be more of an inconvenience rather than a safety issue if somebody did that here in Australia," Dr Stanton said.
The action of GPS jamming is also outright illegal in Australia.
The Australian Communications and Media Authority (ACMA) classifies GPS jammers as prohibited and there are fines up to $330,000 and/or up to two years in prison for possession, operation, supply, or offering to supply such devices.
"Our skies are well protected," Dr Stanton said.
"We've got the laws that restrict the purchase of these things and using these things, and ultimately our pilots are well trained to use conventional navigation aides.
"Our pilots always have the means of navigating and landing safely in Australia."
